Such perforating guns are used in particular in production wells for the exploration and production of crude oil by means of so-called fracking. In fracking, a medium is introduced under pressure, via a delivery line, into deep, porous layers of earth in order thus to release gas or oil bound in the layers of earth. In order to perforate the well or the protective or delivery tube, also referred to as a casing, and to increase the porosity and extend the period of production of a well, subterranean explosions are carried out by means of a perforating gun. A perforating gun here comprises an outer tube which is provided with a multiplicity of depressions, acting as perforations, and in which is arranged an inner part, which has holders carrying explosive charges.
These explosive charges are arranged in the perforating gun such that, when they are detonated, the result is a multiplicity of jets which penetrate the perforations in the outer tube, and the jets run radially into the layer of earth and likewise perforate, or break up, the same. The medium which is to be produced can then be produced more easily and productively through the perforations or as a result of the layers of earth being broken up in this way. On the one hand, it is necessary for the outer tube of such a perforating gun to withstand a high compression pressure, which becomes established on account of the earth masses at depth. On the other hand, it is nevertheless also necessary to ensure that the outer tube is not damaged by these explosions. In particular it has to remain free of deformation, or at least must not undergo inadmissible widening, in the event of the explosions, so that it remains possible for the outer tube or the perforating gun to be removed from the well or from the casing. Such a perforating gun is described, for example, in U.S. Pat. No. 8,794,326 B2.
U.S. 2014/0041515 A1 and WO 2014/182304 A1 deal with the optimization of the design and the production of the depressions and/or perforations in the outer tube of the perforating gun.
U.S. 2002/0189483 A1 describes the mechanical loading to which the outer tube is subjected during detonation of the explosive charges of a perforating gun and during propagation of the jets. During the propagation of the pressure waves by way of the jets making contact with the outer tube, there is the problem of the outer tube being damaged and therefore of the removal of the outer tube, or of the perforating gun as a whole, from the well or casing being difficult as a result of the outer contour of the outer tube of the perforating gun being changed. U.S. 2002/0189483 A1 thus proposes optimization of the design of the depressions or perforations in order to have a positive influence on the jet propagation itself and on the propagation of the pressure waves. However, it is also the case here that satisfactory results are not achieved, since the outer contour of the outer tube of the perforating gun can still be damaged, and therefore the removal of the perforating gun from the well continues to be a problem. Furthermore, the explosions initiate cracks on the outer contour of the outer tube of the perforating gun, and said cracks can result in deformation of the outer contour of the outer tube.